Scanning–tunneling microscopy and break-junction spectroscopy on the superconducting Fe(Se, Te) single crystal

We have studied various Fe1.01Se1−xTex (x = 0.2–1.0) single crystals using low-temperature scanning–tunneling microscopy (STM) and break-junction (BJ) techniques. From the STM measurements at 4.9 K, we can identify the Se and Te atomic sites as darker and brighter spots in the topography, respectively, which correlate well with the bulk composition rates from EPMA (electron-probe micro-analyzer) analysis. The BJ measurements of Fe1.01Se0.5Te0.5 showed the superconducting gap structure, giving the gap value 2Δ ≈ 3 meV at 4 K. By adopting the local Tc = 10 K probed at the junction, the characteristic ratio 2Δ/kBTc = 3.4–3.7 is obtained, which is almost consistent with the BCS prediction.

► We have synthesized Fe1.01Se1−xTex (x = 0.2–1.0) single crystals. ► All the samples were characterized by EPMA and resistivity measurements. ► Distinct surface atomic arrangements were observed by STM for all the samples. ► We were able to identify the Se and Te atoms in the STM surface topography. ► BCS-like superconducting gap was obtained by the break-junction technique.